245/40R19 vs 255/40R19
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/40R19 | 255/40R19 | Change |
|---|---|---|---|
| Overall height | 26.7" | 27.0" | +1.2 % |
| Sidewall | 3.86" | 4.02" | +4.1 % |
| Section width | 245 mm | 255 mm | +4.1 % |
| Circumference | 83.9" | 84.9" | +1.2 % |
| Revs per mile | 755 | 746 | -1.2 % |
| Axle height | 13.36" | 13.52" | +4.0 mm |
| Approved rim width | 7–9" | 7–9.5" | overlap 7–9" |
Both are approved on a rim 7" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 245/40R19. Fit 255/40R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,118 on the road, so it under-counts by 118. At a true 70 mph the first turns 881 times a minute, the second 870.
What drivers reported
245/40R19 carries 34 complaints. Nobody has filed one naming 255/40R19.